977 - AMPs Drop When Charging with 12V DC  
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All Forums >> Radios, Batteries, Clubhouse and more >> Batteries & Chargers >> MRC Charger Product Support (i.e. Super Brain, etc) >> 977 - AMPs Drop When Charging with 12V DC
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977 - AMPs Drop When Charging with 12V DC - 2/15/2008 2:47:47 PM   
tarpon6


 

Posts: 2
Joined: 1/3/2008
From: Cape Coral, FL, USA
Status: offline 		When charging my 3 cell 11.1V 2200 mah lipos or my 8 cell 1400 mah NiMH batteries the amps drop from the initial setting. I am charging all at 2 amps, setting the right number of cells, pushing start on the number of cells screen, and it reads Lipo on the lipos. I start at 2 amps and immediately they start dropping.. 1.8, 1.5, 1.4, .8, .6..... Doesn't seem to happen when using the AC power supply. This is not good when I'm at the field and want to charge quickly. I have tried different batteries as the power source..
       Post #: 1

RE: 977 - AMPs Drop When Charging with 12V DC - 2/15/2008 9:39:34 PM   
guver


 

Posts: 8768
Joined: 3/7/2003
From: LaGrange, OH, USA
Status: offline 		Hi Welcome to RCU and the MRC support forum. I don't represent MRC, but they let me help out and I can tell what it's doing.

Since the 977 is close to it's max voltage on outpuit with 8 cells of 3S the input voltage is a bit too low to get full current. Any charge with an output max voltage of around 12 -14 volts needs a couple more volts on the input to get full current.

An increased input voltage is in order (it may be ok to start the vehicle?) If so you would notice an imedite increase in the current. To put it another way : the input voltage is too close to the desired output voltage.

If you're limited to a certain battery and it is full charged then a couple other things will help.
Large, short leads going into the charger and large/short leads going to the rc battery.

Hope this helps out and if you were to use a 2S or 7 cell battery the trouble would completely go away.

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(in reply to tarpon6)
       Post #: 2

RE: 977 - AMPs Drop When Charging with 12V DC - 2/16/2008 9:33:41 PM   
tarpon6


 

Posts: 2
Joined: 1/3/2008
From: Cape Coral, FL, USA
Status: offline 		Does this apply to all chargers? Or might a different charger be able to deliver a constant 2-3 amps from a 12v dc source with 8 cell NiMH or 3s Lipo?

(in reply to guver)
       Post #: 3

RE: 977 - AMPs Drop When Charging with 12V DC - 2/16/2008 9:44:14 PM   
guver


 

Posts: 8768
Joined: 3/7/2003
From: LaGrange, OH, USA
Status: offline 		It would apply to all chargers with a 7,8,9 cell limit since the battery voltage is around what a 12 volt battery is. Most any charger with a 10 + cell limit it will not necessarily apply to. They have the ability to output higher voltage than is coming in.

The 989 will output 39 volts with less than 12 volts input. Many chargers have the 6,7 cell limit and many many have an 8 cell limit (probably for this reason)

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(in reply to tarpon6)
       Post #: 4

RE: 977 - AMPs Drop When Charging with 12V DC - 2/19/2008 2:40:18 PM   
Tim@MRC


 

Posts: 345
Joined: 7/24/2006
From: Edison, NJ, USA
Status: offline 		Guver is right, the output voltage of the charger is limited to the input voltage. Starting the car would increase the input voltage to approximately 14-14.5 volts, which would definitely increase the output amperage for the 3 cell LiPos. Like he said, all chargers that are rated for 8 cells NiCd/NiMH, you will notice an amperage drop as the battery voltage begins to approach the output voltage of the charger.

(in reply to guver)
       Post #: 5

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All Forums >> Radios, Batteries, Clubhouse and more >> Batteries & Chargers >> MRC Charger Product Support (i.e. Super Brain, etc) >> 977 - AMPs Drop When Charging with 12V DC
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